1. Field of the Invention
This invention relates generally to speaker systems. More specifically, this invention relates to speaker systems used by audio enthusiasts interested in recreating a sound field with a high degree of quality.
2. Description of the Related Art
Throughout the years, consumers have purchased acoustic playback systems for their entertainment, and these systems vary greatly in size, cost, appearance, and fidelity. A select group of consumers (audio enthusiasts) takes particular pride and enjoyment in their high fidelity acoustic playback systems, including their speaker systems. A true test characteristic and goal of a high fidelity acoustic playback system is the ability to reproduce a sound field with a high degree of accuracy.
The theoretical goal of an acoustic playback system is to reproduce the sound field as when it was originally made. To properly design a playback system, it must first be understood how sound fields are recorded and the environment in which the playback will typically occur.
When sounds are created, the sound waves (energy) are radiated in all directions. This total energy can be considered a sound field. A person listening to the original acoustical event is of small size in relation to the size of the total sound field, and could be considered as a point in the sound field. Likewise, when sounds are recorded, they are captured with a microphone, which is also of small size in relation to the sound field and would also be considered as a point in the sound field.
When reproducing such sounds, the optimum playback mechanism is through an acoustical point source. A point source is a theoretical, infinitely small sound source capable of reproducing all frequencies from the same physical location. One example of a point source is a single transducer. Unfortunately, no single transducer can reproduce sounds uniformly at typical listening levels over the entire audio frequency spectrum with minimal distortion. For example, it is well known in the art that a large low frequency transducer, such as a woofer, has difficulty generating high frequency sounds. Similarly, it is well known that a small high frequency transducer, such as a tweeter, has difficulty generating low frequency sounds.
To overcome some of the limitations of single transducer systems, one might use multiple transducers of different sizes to reproduce the full range of the audible frequency spectrum. In one approach, a speaker system includes a small high frequency transducer near the top of the mounting board and one or more larger transducers near the bottom. Such systems are commonly called xe2x80x9ctwo-wayxe2x80x9d or xe2x80x9cthree-wayxe2x80x9d speaker systems. With this approach, however, the speaker system no longer emulates a point source, and a human ear can be sensitive to the direction of sound. A listener with a discerning ear can notice the different physical locations of these transducers. This arrangement also yields different path lengths from each transducer to the listener. Thus, the respective sounds do not arrive all at the same time. The result does not sound like the original source.
In addition, enthusiasts"" acoustic playback systems are typically used indoors, and when these systems reproduce sound, the generated sound waves travel in all directions. Ideally, the listener should hear only the sound waves traveling towards him. In actuality, the listener hears these sound waves and those reflected waves which bounce off the room""s surfaces, primarily the walls, floor, and ceiling. Since these reflected sound waves have traveled a longer distance to the listener than the direct waves, they are delayed in relation to the direct sound. The waveform heard by the listener is therefore distorted by the combination of the direct and reflected sound. Thus, the listener is not hearing the sound field as it was originally generated or recorded. The ideal playback system would direct its sound only to the listener and not to the entire room. An example would be the use of earphones.
The efficient reproduction of low frequency sound generally requires physically large transducers to displace the necessary air volume. Large transducers can accurately reproduce low frequencies with minimal distortion, but with midrange or high frequencies, they usually exhibit large resonant peaks and associated distortions. Smaller transducers exhibit fewer resonant peaks in the midrange, but at the expense of limited low frequency reproduction capability. One approach that is used to accurately reproduce both low and midrange frequencies is to substitute a plurality or array of medium size transducers for the larger transducer. However, using conventional arrays that feature a plurality of transducers over a common frequency range will produce acoustical interference patterns and an increased prevalence of side lobes. These conventional arrays direct a portion of their sound towards the listener (main lobe) and a portion of their sound towards the sides (side lobes). When placed in a room, the sound waves in the side lobes reflect from surfaces such as walls, the ceiling, and the floor (room reflections). The reflected sound waves interact either constructively or destructively, depending on the delay time and frequency, with the direct sound waves. The listener is presented with a sound field that is a combination of the direct sound from the main lobe and the reflected and delayed sound from the side lobes. Although the speaker system may have exhibited a flat frequency response in an anechoic chamber, the frequency response in the room at the listener is anything but flat, with pronounced variations in the response. The result is the listener hears a severely distorted sound field that bears little resemblance to the original event.
In the quest for realism, audio enthusiasts have taken inconvenient measures to reduce the distortion due to reflections. To maintain the integrity of the reproduced sound field with a traditional speaker system, an audio enthusiast carefully positions a speaker system within a room. The strategic positioning of the speaker system enables the audio enthusiast to hear more of the direct sound and less of the reflected sounds. Some audio enthusiasts also take the expensive step of placing acoustical absorptive materials on the walls to further reduce the energy of the reflected sound waves.
Few conventional speaker systems approach an ideal of a high efficiency point source directional loudspeaker system. In fact, most conventional speaker systems are low in efficiency, lack phase coherency, and do not act as an apparent point source system. A speaker system in accordance with the present invention closely emulates a single point source. Embodiments of the present invention achieve this result by an advantageous arrangement of transducers. The arrangement of transducers minimizes the amplitude of the sound waves that can cause room reflections and the resultant distortion therein.
A plurality of transducers are attached to the front side of an enclosure such that the centers of the transducers are equally spaced along both horizontal and vertical axes and yet staggered so that the centers of the transducers form at least two parallel lines. Preferably, the transducers in the plurality of transducers are all identical medium size low frequency transducers (woofers). Preferably, the speaker system also includes a high frequency transducer (tweeter) mounted in the center of the plurality of transducers and further includes a grille to cover the front of the speaker system.
A speaker system includes four transducers mounted in a square pattern on the front of an enclosure. The square pattern formed by the transducers is rotated at an angle within the range of 18.4 to 31.0 degrees and is preferably rotated at an angle of 26.57 degrees. Preferably, the four transducers are identical medium size woofers that are also wired in series-parallel configuration. Preferably, the speaker system also includes a tweeter and a crossover network. The tweeter may be set back in the enclosure relative to the other transducers to synchronize sound waves emitted by the tweeter with sound waves emitted by the four transducers in an overlapping range of frequencies. A horn may also be used with the tweeter to set back the tweeter in the enclosure and to match the sound level of the tweeter to that of the four transducers. In one embodiment, the enclosure is a sealed box.
Another speaker system includes four transducers mounted in a square pattern on the front of the enclosure. The enclosure is rotatable to allow the square pattern formed by the four transducers to achieve an angle including 26.57 degrees. The enclosure includes a mounting device to hold the speaker system at a particular angle. In some embodiments, the speaker system can freely rotate to any angle. The speaker system may include a speaker stand serving as the mounting device. Preferably, the speaker system indicates when the square pattern has formed an angle of approximately 26.57 degrees.
Another speaker system includes an arrangement of enclosures. The enclosures can have one or more transducers per enclosure, and the enclosures attach so that the centers of the transducers form a square pattern rotated at an angle within the range of 18.4 to 31.0 degrees with respect to a horizontal axis. Such a speaker system includes four separate enclosures with one speaker each. The enclosures can be attached to each other by glue or other means and can be attached to a frame as well. Preferably, a decorative grille covers the transducers.
A method of using an angled speaker stand to rotate a speaker enclosure as viewed from the perspective of the listener. Using this method, a typical speaker array may attain benefits disclosed herewith. Such a stand may also include a leg for elevating the speaker array and an additional member for retaining the speaker array on the top of the speaker stand.